EP 0 589 158 B1 discloses a lock having a latch which, when operatively connected to a shackle, keeps a vehicle door in the closed position. A detent pawl and the latch are in a positively locking connection in the closed state. The positively locking connection between latch and detent pawl can be broken by means of an electric actuating drive by virtue of the electric actuating drive exerting a force on the detent pawl which brings about a pivot movement by the detent pawl and breaks the positively locking connection between latch and detent pawl.
The electric actuating drive is supplied with electric current by means of a controller which is powered by means of the vehicle battery. The signal to open the motor vehicle door is supplied to the controller by two microswitches which are operated by means of the outer door handle or the inner door handle of the motor vehicle door. These signals are used by the controller to enable the supply of current to the electric actuating drive.
For safety reasons, the controller has a relay connected to it which interrupts the supply of current to the electric actuating drive when the vehicle is not stationary, for example, which means that the electric actuating drive cannot be actuated by the central motor vehicle electronics.
DE 103 60 422 A1 shows a circuit in which the outer door handle and the inner door handle each operate a sensor. The sensor comprises two switches and two resistors. A respective switch and resistor are connected in series, with the series-connected resistor/switch elements being arranged in parallel. The resistors are used for resistance coding, wherein the switches complete the circuit. On the basis of this resistance coding, the controller can recognize an erroneous signal and react accordingly. Furthermore, when a line is disconnected, the signal can be passed on to the controller via the second parallel-led resistor/switch element. The controller is then connected directly to the lock or to the electric actuating drive.
Both EP 0 589 158 B1 and DE 103 60 422 A1 involve the controller being connected directly to the electric actuating drive. As such, it is possible to open a motor vehicle door inadvertently on the basis of an erroneous signal from the controller. In this case, the motor vehicle door could open during the journey, for example, and put both the vehicle occupants and vehicles in proximity at risk. In order to avoid this, DE 100 42 191 A1 describes a lock which mechanically couples the electric actuating drive when the inner door handle or outer door handle is operated. To this end, the electric actuating element and the detent pawl have a mechanical coupling arranged between them which is operated by means of the outer door handle and/or the inner door handle. When the outer door handle or inner door handle is not being operated, the mechanical connection between the electric actuating element and the detent pawl is interrupted. If the electric actuating element is supplied with current on account of an error in the controller, the movement comes to nothing. The motor vehicle door does not open. If the inner door handle and/or the outer door handle is operated, the mechanical connection between the electric actuating element and the detent pawl is completed (coupled). At the same time, the operation of the outer door handle and/or the inner door handle sends a signal to the controller, which signal supplies current to the electric actuating element. Since the mechanical connection between the actuating element and the detent pawl is complete (coupled), the movement is transmitted to the detent pawl and the motor vehicle door is opened. However, a mechanical coupling comprises a plurality of elements which are sensitive to tolerance and the assembly of which is complex. Furthermore, a mechanical coupling produces noise and is sensitive to dirt and icing up.